Multichannel Heat Exchanger

ABSTRACT

Heating, ventilation, air conditioning, and refrigeration (HVAC&amp;R) systems and heat exchangers are provided that include multichannel tube and fin configurations designed to promote the release of condensate. The multichannel tubes may have a curved, round, or airfoil shape, and may be used with plate or corrugated fins. In certain embodiments, corrugated fins may be brazed to multichannel tubes and then trimmed to form individual fin structures. Double header configurations also may be employed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from and the benefit of U.S. Provisional Application Ser. No. 61/080,079, entitled “Multichannel Heat Exchanger”, filed Jul. 11, 2008, which is hereby incorporated by reference.

BACKGROUND

The invention relates generally to tube, fin, and header configurations for multichannel heat exchangers.

Heat exchangers are used in heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems. Multichannel heat exchangers generally include multichannel tubes for flowing refrigerant through the heat exchanger. Each multichannel tube may contain several individual flow channels, or paths. Fins may be positioned between the tubes to facilitate heat transfer between refrigerant contained within the flow paths and an external fluid passing over the tubes. Moreover, multichannel heat exchangers may be used in small tonnage systems, such as residential systems, or in large tonnage systems, such as industrial chiller systems.

The transfer of heat within multichannel heat exchangers is generally driven by flow of an external fluid passing through the heat exchanger. Typically, as the fluid passes through the heat exchanger, the fluid contacts the individual multichannel tubes and flows across each tube, contacting first a leading edge of the tube, flowing across the width of the tube, and contacting last a trailing edge of the tube. Heat transfer between the external fluid and the refrigerant is dependent on, among other things, the temperature difference between the external fluid flowing across the multichannel tubes and the refrigerant flowing inside the multichannel tubes. For example, in an evaporator, an external fluid, such as air, may flow over the multichannel tubes. The refrigerant flowing inside the multichannel tubes is generally cooler than the air and, therefore, absorbs heat from the air. The exchange of heat may produce cooled air exiting the heat exchanger and warmed refrigerant flowing within the heat exchanger. In an example employing a condenser, an external fluid, such as air, may flow over multichannel tubes containing a refrigerant that is generally warmer than the air. As the air flows across the tubes, the internal refrigerant transfers heat to the air. The exchange of heat may produce warmed air exiting the heat exchanger and cooled refrigerant flowing within the heat exchanger.

An issue with conventional multichannel heat exchangers is their tendency to hold condensate between the tubes (and cooling fins). Due to the relatively small interstices between these elements, water tends to collect and reduces the thermal transfer capabilities by closing flow paths for air. This is particularly problematic for heat exchangers functioning as evaporators outside (i.e., in a heat pump operating in heat pump mode). Condensate can freeze when outside temperatures drop, and while the condensate may be defrosted by various means, it typically does not clear and will simply refreeze, significantly reducing the effectiveness of the system.

SUMMARY

The present invention relates to heat exchangers with tube, fin, and header configurations designed to respond to such needs. The concepts described below may be employed in various designs of HVAC&R systems, including air conditioners, heat pumps, light commercial industrial, chiller, and other systems and system components. The configurations may be particularly well-suited to heat exchangers functioning as outdoor evaporation units. The embodiments may include curved tubes, aerodynamic tubes, round tubes, fins, and headers intended to promote the release of condensate from a heat exchanger.

DRAWINGS

FIG. 1 is an illustration of an exemplary embodiment of a commercial or industrial HVAC&R system that employs heat exchangers.

FIG. 2 is an illustration of an exemplary embodiment of a residential HVAC&R system that employs heat exchangers.

FIG. 3 is an exploded view of the outdoor unit shown in FIG. 2.

FIG. 4 is a diagrammatical overview of an exemplary air conditioning system that may employ one or more heat exchangers.

FIG. 5 is a diagrammatical over of an exemplary heat pump system that may employ one or more heat exchangers.

FIG. 6 is a perspective view of an exemplary embodiment of a heat exchanger containing multichannel tubes.

FIG. 7 is a perspective view of an exemplary multichannel tube employed in the heat exchanger of FIG. 6.

FIG. 8 is a detailed perspective view of a section of multichannel tubes and fins employed in the heat exchanger of FIG. 6.

FIG. 9 is a detailed perspective view of another exemplary embodiment of multichannel tubes and fins that may be employed in a heat exchanger.

FIG. 10 is a detailed perspective view of an exemplary tube configuration that may be employed in a heat exchanger.

FIG. 11 is a detailed perspective view of an exemplary multichannel tube.

FIG. 12 is a detailed perspective view of an exemplary multichannel tube.

FIG. 13 is a detailed perspective view of an exemplary multichannel tube.

FIG. 14 is a detailed perspective view of an exemplary multichannel tube.

FIG. 15 is a detailed perspective view of an exemplary multichannel tube.

FIG. 16 is a detailed perspective view of an exemplary multichannel tube.

FIG. 17 is a detailed perspective view of an exemplary multichannel tube.

FIG. 18 is a detailed perspective view of an exemplary multichannel tube.

FIG. 19 is a detailed perspective view of an exemplary tube and fin configuration.

FIG. 20 is a detailed perspective view of another exemplary tube and fin configuration.

FIG. 21 is a detailed perspective view of an exemplary embodiment of a fin structure that may be employed in a heat exchanger.

FIG. 22 is a detailed perspective view of the fin structure shown in FIG. 21 attached to multichannel tubes.

FIG. 23 is a detailed perspective view of the fin structure shown in FIG. 22 after trimming of the fins.

FIG. 24 is a detailed perspective view of an exemplary fin and tube configuration.

FIG. 25 is a detailed perspective view of the fin and tube configuration shown in FIG. 24 after trimming of the fins.

FIG. 26 is a detailed perspective view of an exemplary tube and fin configuration with angled fins.

FIG. 27 is a detailed perspective view of an exemplary embodiment of a heat exchanger employing a double header.

FIG. 28 is a top sectional view of the heat exchanger shown in FIG. 27.

DETAILED DESCRIPTION

FIGS. 1 and 2 depict exemplary applications for heat exchangers. Such systems, in general, may be applied in a range of settings, both within the HVAC&R field and outside of that field. In presently contemplated applications, however, heat exchanges may be used in residential, commercial, light industrial, industrial, and in any other application for heating or cooling a volume or enclosure, such as a residence, building, structure, and so forth. Moreover, the heat exchanges may be used in industrial applications, where appropriate, for basic refrigeration and heating of various fluids.

FIG. 1 illustrates an exemplary application, in this case an HVAC&R system for building environmental management that may employ heat exchangers. A building 10 is cooled by a system that includes a chiller 12 and a boiler 14. As shown, chiller 12 is disposed on the roof of building 10 and boiler 14 is located in the basement; however, the chiller and boiler may be located in other equipment rooms or areas next to the building. Chiller 12 is an air cooled or water cooled device that implements a refrigeration cycle to cool water. Chiller 12 may be a stand-alone unit or may be part of a single package unit containing other equipment, such as a blower and/or integrated air handler. Boiler 14 is a closed vessel that includes a furnace to heat water. The water from chiller 12 and boiler 14 is circulated through building 10 by water conduits 16. Water conduits 16 are routed to air handlers 18, located on individual floors and within sections of building 10. Air handlers 18 are coupled to ductwork 20 that is adapted to distribute air between the air handlers and may receive air from an outside intake (not shown). Air handlers 18 include heat exchangers that circulate cold water from chiller 12 and hot water from boiler 14 to provide heated or cooled air. Fans, within air handlers 18, draw air through the heat exchangers and direct the conditioned air to environments within building 10, such as rooms, apartments or offices, to maintain the environments at a designated temperature. A control device, shown here as including a thermostat 22, may be used to designate the temperature of the conditioned air. Control device 22 also may be used to control the flow of air through and from air handlers 18. Other devices may, of course, be included in the system, such as control valves that regulate the flow of water and pressure and/or temperature transducers or switches that sense the temperatures and pressures of the water, the air, and so forth. Moreover, control devices may include computer systems that are integrated with or separate from other building control or monitoring systems, and even systems that are remote from the building.

FIG. 2 illustrates a residential heating and cooling system. In general, a residence 24, will include refrigerant conduits 26 that operatively couple an indoor unit 28 to an outdoor unit 30. Indoor unit 28 may be positioned in a utility room, an attic, a basement, and so forth. Outdoor unit 30 is typically situated adjacent to a side of residence 24 and is covered by a shroud to protect the system components and to prevent leaves and other contaminants from entering the unit. Refrigerant conduits 26 transfer refrigerant between indoor unit 28 and outdoor unit 30, typically transferring primarily liquid refrigerant in one direction and primarily vaporized refrigerant in an opposite direction.

When the system shown in FIG. 2 is operating as an air conditioner, a coil in outdoor unit 30 serves as a condenser for recondensing vaporized refrigerant flowing from indoor unit 28 to outdoor unit 30 via one of the refrigerant conduits 26. In these applications, a coil of the indoor unit, designated by the reference numeral 32, serves as an evaporator coil. Evaporator coil 32 receives liquid refrigerant (which may be expanded by an expansion device, not shown) and evaporates the refrigerant before returning it to outdoor unit 30.

Outdoor unit 30 draws in environmental air through its sides as indicated by the arrows directed to the sides of the unit, forces the air through the outer unit coil by a means of a fan (not shown), and expels the air as indicated by the arrows above the outdoor unit. When operating as an air conditioner, the air is heated by the condenser coil within the outdoor unit and exits the top of the unit at a temperature higher than it entered the sides. Air is blown over indoor coil 32 and is then circulated through residence 24 by means of ductwork 20, as indicated by the arrows entering and exiting ductwork 20. The overall system operates to maintain a desired temperature as set by thermostat 22. When the temperature sensed inside the residence is higher than the set point on the thermostat (plus a small amount), the air conditioner will become operative to refrigerate additional air for circulation through the residence. When the temperature reaches the set point (minus a small amount), the unit will stop the refrigeration cycle temporarily.

When the unit in FIG. 2 operates as a heat pump, the roles of the coils are simply reversed. That is, the coil of outdoor unit 30 will serve as an evaporator to evaporate refrigerant and thereby cool air entering outdoor unit 30 as the air passes over the outdoor unit coil. Indoor coil 32 will receive a stream of air blown over it and will heat the air by condensing a refrigerant.

FIG. 3 illustrates a partially exploded view of one of the units shown in FIG. 2, in this case outdoor unit 30. Unit 30 includes a shroud 34 that surrounds the sides of unit 30 to protect the system components and to prevent leaves and other contaminates from entering unit 30. Adjacent to shroud 34 is a heat exchanger 36. As shown, heat exchanger 36 includes multichannel tubes and plate fins. However, in other embodiments, the heat exchanger may include a multichannel tube heat exchanger with corrugated fins, or other suitable type fins. A cover 38 encloses a top portion of heat exchanger 36. Foam 40 is disposed between cover 38 and heat exchanger 36. A fan 42 is located within an opening of cover 38 and is powered by a motor 44. A wire way 46 may be used to connect motor 44 to a power source. A fan guard 48 fits within cover 38 and is disposed above the fan to prevent objects from entering the fan.

Heat exchanger 36 is mounted on a base pan 50. Base pan 50 provides a mounting surface and structure for the internal components of unit 30. A compressor 52 is disposed within the center of unit 30 and is connected to another unit within the HVAC&R system, for example an indoor unit, by connections 54 and 56 that connect to conduits circulating refrigerant within the HVAC&R system. A control box 58 houses the control circuitry for outdoor unit 30 and is protected by a cover 60. A panel 62 may be used to mount control box 58 to unit 30.

Refrigerant enters unit 30 through vapor connection 54 and flows through a conduit 64 into compressor 52. The vapor may be received from the indoor unit (not shown). After undergoing compression in compressor 52, the refrigerant exits compressor 52 through a conduit 66 and enters heat exchanger 36 through inlet 68. Inlet 68 directs the refrigerant into header 70. From header 70, the refrigerants flows through heat exchanger 36 to header 72. From header 72 the refrigerant flows back through heat exchanger 36 and exits through an outlet 74 disposed on header 70. After exiting heat exchanger 36, the refrigerant flows through conduit 76 to liquid connection 56 to return to the indoor unit where the process may begin again.

FIG. 4 illustrates an air conditioning system 78, which may employ multichannel tube heat exchangers. Refrigerant flows through system 78 within closed refrigeration loop 80. The refrigerant may be any fluid that absorbs and extracts heat. For example, the refrigerant may be hydrofluorocarbon (HFC) based R-410A, R-407, or R-134a, or it may be carbon dioxide (R-744A) or ammonia (R-717). Air conditioning system 78 includes control devices 82 that enable the system to cool an environment to a prescribed temperature.

System 78 cools an environment by cycling refrigerant within closed refrigeration loop 80 through a condenser 84, a compressor 86, an expansion device 88, and an evaporator 90. The refrigerant enters condenser 84 as a high pressure and temperature vapor and flows through the multichannel tubes of the condenser. A fan 92, which is driven by a motor 94, draws air across the multichannel tubes. The fan may push or pull air across the tubes. As the air flows across the tubes, heat transfers from the refrigerant vapor to the air, producing heated air 96 and causing the refrigerant vapor to condense into a liquid. The liquid refrigerant then flows into an expansion device 88 where the refrigerant expands to become a low pressure and temperature liquid. Typically, expansion device 88 will be a thermal expansion valve (TXV); however, according to other exemplary embodiments, the expansion device may be an orifice or a capillary tube. After the refrigerant exits the expansion device, some vapor refrigerant may be present in addition to the liquid refrigerant.

From expansion device 88, the refrigerant enters evaporator 90 and flows through the evaporator multichannel tubes. A fan 98, which is driven by a motor 100, draws air across the multichannel tubes. As the air flows across the tubes, heat transfers from the air to the refrigerant liquid, producing cooled air 102 and causing the refrigerant liquid to boil into a vapor. According to certain embodiments, the fan may be replaced by a pump that draws fluid across the multichannel tubes.

The refrigerant then flows to compressor 86 as a low pressure and temperature vapor. Compressor 86 reduces the volume available for the refrigerant vapor, consequently, increasing the pressure and temperature of the vapor refrigerant. The compressor may be any suitable compressor such as a screw compressor, reciprocating compressor, rotary compressor, swing link compressor, scroll compressor, or turbine compressor. Compressor 86 is driven by a motor 104 that receives power from a variable speed drive (VSD) or a direct AC or DC power source. According to an exemplary embodiment, motor 104 receives fixed line voltage and frequency from an AC power source although in certain applications the motor may be driven by a variable voltage or frequency drive. The motor may be a switched reluctance (SR) motor, an induction motor, an electronically commutated permanent magnet motor (ECM), or any other suitable motor type. The refrigerant exits compressor 86 as a high temperature and pressure vapor that is ready to enter the condenser and begin the refrigeration cycle again.

The control devices 82, which include control circuitry 106, an input device 108, and a temperature sensor 110, govern the operation of the refrigeration cycle. Control circuitry 106 is coupled to the motors 94, 100, and 104 that drive condenser fan 92, evaporator fan 98, and compressor 86, respectively. Control circuitry 106 uses information received from input device 108 and sensor 110 to determine when to operate the motors 94, 100, and 104 that drive the air conditioning system. In certain applications, the input device may be a conventional thermostat. However, the input device is not limited to thermostats, and more generally, any source of a fixed or changing set point may be employed. These may include local or remote command devices, computer systems and processors, and mechanical, electrical and electromechanical devices that manually or automatically set a temperature-related signal that the system receives. For example, in a residential air conditioning system, the input device may be a programmable 24-volt thermostat that provides a temperature set point to the control circuitry. Sensor 110 determines the ambient air temperature and provides the temperature to control circuitry 106. Control circuitry 106 then compares the temperature received from the sensor to the temperature set point received from the input device. If the temperature is higher than the set point, control circuitry 106 may turn on motors 94, 100, and 104 to run air conditioning system 78. The control circuitry may execute hardware or software control algorithms to regulate the air conditioning system. According to exemplary embodiments, the control circuitry may include an analog to digital (A/D) converter, a microprocessor, a non-volatile memory, and an interface board. Other devices may, of course, be included in the system, such as additional pressure and/or temperature transducers or switches that sense temperatures and pressures of the refrigerant, the heat exchangers, the inlet and outlet air, and so forth.

FIG. 5 illustrates a heat pump system 112 that may employ multichannel tube heat exchangers. Because the heat pump may be used for both heating and cooling, refrigerant flows through a reversible refrigeration/heating loop 114. The refrigerant may be any fluid that absorbs and extracts heat. The heating and cooling operations are regulated by control devices 116.

Heat pump system 112 includes an outside coil 118 and an inside coil 120 that both operate as heat exchangers. Each coil may function as an evaporator or a condenser depending on the heat pump operation mode. For example, when heat pump system 112 is operating in cooling (or “AC”) mode, outside coil 118 functions as a condenser, releasing heat to the outside air, while inside coil 120 functions as an evaporator, absorbing heat from the inside air. When heat pump system 112 is operating in heating mode, outside coil 118 functions as an evaporator, absorbing heat from the outside air, while inside coil 120 functions as a condenser, releasing heat to the inside air. A reversing valve 122 is positioned on reversible loop 114 between the coils to control the direction of refrigerant flow and thereby to switch the heat pump between heating mode and cooling mode.

Heat pump system 112 also includes two metering devices 124 and 126 for decreasing the pressure and temperature of the refrigerant before it enters the evaporator. The metering devices also regulate the refrigerant flow entering the evaporator so that the amount of refrigerant entering the evaporator equals, or approximately equals, the amount of refrigerant exiting the evaporator. The metering device used depends on the heat pump operation mode. For example, when heat pump system 112 is operating in cooling mode, refrigerant bypasses metering device 124 and flows through metering device 126 before entering inside coil 120, which acts as an evaporator. In another example, when heat pump system 112 is operating in heating mode, refrigerant bypasses metering device 126 and flows through metering device 124 before entering outside coil 118, which acts as an evaporator. According to other exemplary embodiments, a single metering device may be used for both heating mode and cooling mode. The metering devices typically are thermal expansion valves (TXV), but also may be orifices or capillary tubes.

The refrigerant enters the evaporator, which is outside coil 118 in heating mode and inside coil 120 in cooling mode, as a low temperature and pressure liquid. Some vapor refrigerant also may be present as a result of the expansion process that occurs in metering device 124 or 126. The refrigerant flows through multichannel tubes in the evaporator and absorbs heat from the air changing the refrigerant into a vapor. In cooling mode, the indoor air flowing across the multichannel tubes also may be dehumidified. The moisture from the air may condense on the outer surface of the multichannel tubes and consequently be removed from the air.

After exiting the evaporator, the refrigerant passes through reversing valve 122 and into a compressor 128. Compressor 128 decreases the volume of the refrigerant vapor, thereby, increasing the temperature and pressure of the vapor. The compressor may be any suitable compressor such as a screw compressor, reciprocating compressor, rotary compressor, swing link compressor, scroll compressor, or turbine compressor.

From compressor 128, the increased temperature and pressure vapor refrigerant flows into a condenser, the location of which is determined by the heat pump mode. In cooling mode, the refrigerant flows into outside coil 118 (acting as a condenser). A fan 130, which is powered by a motor 132, draws air across the multichannel tubes containing refrigerant vapor. According to certain exemplary embodiments, the fan may be replaced by a pump that draws fluid across the multichannel tubes. The heat from the refrigerant is transferred to the outside air causing the refrigerant to condense into a liquid. In heating mode, the refrigerant flows into inside coil 120 (acting as a condenser). A fan 134, which is powered by a motor 136, draws air across the multichannel tubes containing refrigerant vapor. The heat from the refrigerant is transferred to the inside air causing the refrigerant to condense into a liquid.

After exiting the condenser, the refrigerant flows through the metering device (124 in heating mode and 126 in cooling mode) and returns to the evaporator (outside coil 118 in heating mode and inside coil 120 in cooling mode) where the process begins again.

In both heating and cooling modes, a motor 138 drives compressor 128 and circulates refrigerant through reversible refrigeration/heating loop 114. The motor may receive power either directly from an AC or DC power source or from a variable speed drive (VSD). The motor may be a switched reluctance (SR) motor, an induction motor, an electronically commutated permanent magnet motor (ECM), or any other suitable motor type.

The operation of motor 138 is controlled by control circuitry 140. Control circuitry 140 receives information from an input device 142 and sensors 144, 146, and 148 and uses the information to control the operation of heat pump system 112 in both cooling mode and heating mode. For example, in cooling mode, input device 142 provides a temperature set point to control circuitry 140. Sensor 148 measures the ambient indoor air temperature and provides it to control circuitry 140. Control circuitry 140 then compares the air temperature to the temperature set point and engages compressor motor 138 and fan motors 132 and 136 to run the cooling system if the air temperature is above the temperature set point. In heating mode, control circuitry 140 compares the air temperature from sensor 148 to the temperature set point from input device 142 and engages motors 132, 136, and 138 to run the heating system if the air temperature is below the temperature set point.

Control circuitry 140 also uses information received from input device 142 to switch heat pump system 112 between heating mode and cooling mode. For example, if input device 142 is set to cooling mode, control circuitry 140 will send a signal to a solenoid 150 to place reversing valve 122 in an air conditioning position 152. Consequently, the refrigerant will flow through reversible loop 114 as follows: the refrigerant exits compressor 128, is condensed in outside coil 118, is expanded by metering device 126, and is evaporated by inside coil 120. If the input device is set to heating mode, control circuitry 140 will send a signal to solenoid 150 to place reversing valve 122 in a heat pump position 154. Consequently, the refrigerant will flow through the reversible loop 114 as follows: the refrigerant exits compressor 128, is condensed in inside coil 120, is expanded by metering device 124, and is evaporated by outside coil 118.

The control circuitry may execute hardware or software control algorithms to regulate heat pump system 112. According to exemplary embodiments, the control circuitry may include an analog to digital (A/D) converter, a microprocessor, a non-volatile memory, and an interface board.

The control circuitry also may initiate a defrost cycle when the system is operating in heating mode. When the outdoor temperature approaches freezing, moisture in the outside air that is directed over outside coil 118 may condense and freeze on the coil. Sensor 144 measures the outside air temperature, and sensor 146 measures the temperature of outside coil 118. These sensors provide the temperature information to the control circuitry which determines when to initiate a defrost cycle. For example, if either sensor 144 or 146 provides a temperature below freezing to the control circuitry, system 112 may be placed in defrost mode. In defrost mode, solenoid 150 is actuated to place reversing valve 122 in air conditioning position 152, and motor 132 is shut off to discontinue air flow over the multichannel tubes. System 112 then operates in cooling mode until the increased temperature and pressure refrigerant flowing through outside coil 80 defrosts the coil. Once sensor 146 detects that coil 118 is defrosted, control circuitry 140 returns the reversing valve 122 to heat pump position 154. As will be appreciated by those skilled in the art, the defrost cycle can be set to occur at many different time and temperature combinations.

FIG. 6 is a perspective view of an exemplary heat exchanger that may be used in air conditioning system 78, shown in FIG. 4, or heat pump system 112, shown in FIG. 5. The exemplary heat exchanger may be a condenser 84, an evaporator 90, an outside coil 118, or an inside coil 120, as shown in FIGS. 4 and 5. It should be noted that in similar or other systems, the heat exchanger may be used as part of a chiller or in any other heat exchanging application. The heat exchanger includes manifolds 70 and 72 that are connected by multichannel tubes 164. Although 30 tubes are shown in FIG. 6, the number of tubes may vary. The manifolds and tubes may be constructed of aluminum or any other material that promotes good heat transfer. Refrigerant flows from manifold 70 through a set of first tubes 166 to manifold 72. The refrigerant then returns to manifold 70 in an opposite direction through a set of second tubes 168. The first tubes may have the same configuration as the second tubes or the first tubes may have a different configuration from the second tubes. According to other exemplary embodiments, the heat exchanger may be rotated approximately 90 degrees so that the multichannel tubes run vertically between a top manifold and a bottom manifold. Furthermore, the heat exchanger may be inclined at an angle relative to the vertical. Although the multichannel tubes are depicted as having an oblong shape, the tubes may be any shape, such as tubes with a cross-section in the form of a rectangle, square, circle, oval, ellipse, triangle, trapezoid, or parallelogram. According to exemplary embodiments, the tubes may have a diameter ranging from 0.5 mm to 3 mm. It should also be noted that the heat exchanger may be provided in a single plane or slab, or may include bends, corners, contours, and so forth.

According to certain exemplary embodiments, the construction of the first tubes may differ from the construction of the second tubes. Tubes may also differ within each section. For example, the tubes may have different cross sectional shapes or flow path configurations as described below with regard to FIGS. 7 through 36.

Refrigerant enters heat exchanger 36 through inlet 68 and exits the heat exchanger through outlet 74. Although FIG. 6 depicts the inlet at the top of the manifold and the outlet at the bottom of the manifold, the inlet and outlet positions may be interchanged so that the fluid enters at the bottom and exits at the top. The fluid also may enter and exit the manifold from multiple inlets and outlets positioned on bottom, side, or top surfaces of the manifold. Baffles 170 separate the inlet and outlet portions of manifold 70. Although a double baffle 170 is illustrated, any number of one or more baffles may be employed to create separation of the inlet and outlet portions. It should also be noted that according to other exemplary embodiments, the inlet and outlet may be contained on separate manifolds, eliminating the need for a baffle.

Fins 172 are located between multichannel tubes 164 to promote the transfer of heat between the tubes and the environment. According to an exemplary embodiment, the fins are plate fins constructed of aluminum, interference fit or otherwise joined to the tubes, and disposed generally perpendicular to the flow of refrigerant. However, according to other exemplary embodiments, the fins may be made of other materials that facilitate heat transfer and may extend parallel or at varying angles with respect to the flow of the refrigerant. The fins may be louvered fins, corrugated fins, or any other suitable type of fin.

When an external fluid, such as air, flows across multichannel tubes 164, as generally indicated by airflow 174, heat transfer occurs between the refrigerant flowing within tubes 164 and the external fluid. Although the external fluid is shown here as air, other fluids may be used. Airflow 174 flows between fins 166 contacting the upper and lower surfaces of multichannel tubes 164. Airflow 174 may first contact a leading edge 160 of a tube, flow across the tube width, and finally contact a trailing edge 162 of the tube. As the external fluid flows across the tubes, heat is transferred to and from the tubes to the external fluid. For example, in a condenser, the external fluid is generally cooler than the fluid flowing within the multichannel tubes. As the external fluid contacts a multichannel tube, heat is transferred from the refrigerant within the multichannel tube to the external fluid. Consequently, the external fluid is heated as it passes over the multichannel tubes and the refrigerant flowing within the multichannel tubes is cooled. In an evaporator, the external fluid generally has a temperature higher than the refrigerant flowing within the multichannel tubes. Consequently, as the external fluid contacts the leading edge of the multichannel tubes, heat is transferred from the external fluid to the refrigerant flowing in the tubes to heat the refrigerant. The external fluid leaving the multichannel tubes is then cooled because the heat has been transferred to the refrigerant. In certain embodiments, a portion of the external fluid may condense and collect on the tubes and/or fins.

FIG. 7 is a detailed perspective view of one of the tubes 164 shown in FIG. 6. Tube 164 includes flow paths 176 that extend in a generally parallel manner lengthwise through tube 164. Refrigerant flows through tube 164 within flow paths 176 and exchanges heat with an external fluid, such as air, flowing across tube 164, as generally indicated by airflow 178. According to exemplary embodiments, a portion of the external fluid may condense on a surface of tube 164 as condensate 180. Tube 164 includes a generally transverse curvature A intended to promote drainage of condensate 180. As airflow 178 flows across tube 164, airflow 178 may direct condensate 180 towards trailing edge 162 of tube 164. Condensate 180 may drain off tube 164 in the direction of curvature A. In certain exemplary embodiments, a flat tube may be extruded and then the curvature may be formed using a mandrel or other suitable forming process. However, in other exemplary embodiments the tube may be extruded to have a curvature.

FIG. 8 is a detailed perspective view of the tubes 164 and fins 172 illustrated in FIG. 6. The fins may be constructed of aluminum or any other material suitable for promoting good heat transfer. Louvers 184 on fins 172 may allow airflow to pass between fin sections. Tubes 164 are disposed within openings 182 of fins 172. According to certain exemplary embodiments, the openings may be punched into the fins during the forming process. The tubes may then be inserted into the fins and affixed using an interference fit. The interference fit is intended to eliminate the presence brazing material, which may promote condensate collection within the heat exchanger. However, in other embodiments, the tubes may be brazed or otherwise joined to the fins. In certain embodiments, the openings may include collars for receiving the tubes.

FIG. 9 is a detailed perspective view of an alternate tube and fin configuration employing two rows of tubes 164. Fins 186 may include two sets of generally parallel openings 188 and 190. Openings 188 and 190 are staggered to dispose tubes 164 at varying heights within the heat exchanger. For example, the tubes disposed within the first openings 188 are offset from the tubes disposed within the second openings 190. The staggered configuration may promote mixed airflow 178. Airflow 178 exiting the first set of tubes may contact the second set of tubes creating turbulence, and/or a change in direction. The location of the openings 188 and 190 may be configured to influence the direction of airflow 178 exiting the heat exchanger to improve airflow performance. Of course, various tube shapes and configurations may be employed. For example, the tubes may be offset by various amounts, the distance between the openings may vary, or the tubes may be horizontally aligned. In certain embodiments, the first set of tubes may have a different shape than the second set of tubes. Further, openings 188 may be separated by a first distance while openings 190 are separated by another distance. According to other exemplary embodiments, tubes 164 may be inclined relative to the vertical.

FIG. 10 is a detailed perspective view of alternate tubes 192 that may be employed in a heat exchanger. Fins may be disposed between tubes 192, however, as shown, the fins have been omitted for clarity. Tubes 192 include an airfoil shape intended to promote aerodynamic airflow 194 through tubes 192. Condensate 180 may be directed by airflow 194 towards trailing edge 162. The airfoil shape is intended to preserve the laminar boundary layer as air flows across tubes 192. The aerodynamic airflow 194 may reduce the airside pressure drop for the heat exchanger, thereby reducing the power requirement for the fan generating airflow 174. The laminar flow also may provide increased airflow near the surface of tubes 192 to direct condensate 180 across tubes 192. In certain embodiments, condensate 180 may form near leading edge 160. In these embodiments, the distribution of condensate 180 across tubes 192 may reduce frost growth near leading edge 160. Further, the aerodynamic airflow 194 may promote even frost growth across the width of tube 192, thereby increasing the time between defrost cycle and increasing the efficiency of the heat exchanger. After passing between tubes 192, the airflow may exit the heat exchanger as indicated generally by reference numeral 196. Airflow 196 may direct condensate 180 toward trailing edge 162 of tubes 192 and may cause condensate 180 to fall from tubes 192.

FIGS. 11 through 18 depict alternate airfoil tube configurations that may be used in heat exchanger 36, shown in FIG. 6. These figures illustrate exemplary airfoil shapes, exemplary flow path sizes, and exemplary flow path configurations. It should be noted, however, that the shapes, sizes, and configurations shown throughout the figures are not intended to be limiting, and other optimized shapes, sizes, configurations, and combinations therefore may be provided. For example, the flow paths may be any suitable shape, such as circular, oval, rectangular, or square, among others. Moreover, for the sake of the clarity, the flow paths are shown as relatively small with respect to the airfoil cross-section. However, as may be appreciated, the flow paths may occupy a high percentage of the cross-sectional area such that the multichannel tube walls surrounding the airfoils are relatively thin to promote heat transfer between the fluid flowing within the flow paths and the external fluid flowing over the tubes. In another example, the airfoil shapes may be symmetrical, positively cambered, or negatively cambered. In certain exemplary embodiments, the airfoil shapes may be extruded through dies and curved by a mandrel. However, any suitable forming technique may be employed.

FIG. 11 illustrates an alternate airfoil shaped tube 198. Tube 198 is a symmetrical airfoil of a curvature generally indicated by mean camber line B. The cross section of tube 198 includes a maximum thickness C disposed near leading edge 160. The cross section generally tapers from maximum thickness C towards leading edge 160 and trailing edge 162. The flow paths 176 are of generally the same size and are disposed along mean camber line B.

FIG. 12 illustrates a positively cambered airfoil shaped tube 200. As shown by mean camber line B, tube 200 curves generally upward above leading edge 160 and trailing edge 162. The positive camber may promote the drainage of condensate. Tube 200 includes flow paths 202 and 204 of different sizes disposed along mean camber line B. Flow paths 204 are disposed near the outer edges of tube 200 and are of a relatively smaller size then the flow paths 202 disposed near the center of tube 200. The smaller size flow paths 204 allow refrigerant to flow the relatively thinner cross section near the tapered ends of tube 200. In this manner, the different size flow paths 202 and 204 may be configured to maximize the heat transfer between tube 200 and airflow 174. The different size flow paths 202 and 204 also may be used to control the temperature profile of the tube 200. For example, smaller flow paths may be disposed within a thicker section of a tube to create an intended cold spot within the tube to promote an even distribution of frost growth. A larger flow path may be disposed within a thicker section of a tube to decrease the amount of frost growth within that section.

FIG. 13 illustrates another positively cambered airfoil shaped tube 206 employing flow paths 208 disposed at varying heights within the tube cross section. The area of maximum thickness B is located near leading edge 160 and slopes relatively steeply toward leading edge 160. The steep slope may inhibit the collection of condensate near leading edge 160, which may reduce frost growth. Tube 206 includes a thicker section, generally indicated by reference numeral 210, containing a vertically stacked set of flow paths 208 disposed above and below mean camber line B. The stacked flow paths may be used to maximize the flow of refrigerant within tube 206. The remaining flow paths 208 are disposed along mean camber line B. However, according to other exemplary embodiments, multiple sets of stacked flow paths may be included. Further, any number of flow paths may be disposed above and below mean camber line B in staggered or stacked configurations to maximize the flow of refrigerant within the tube.

FIGS. 14 through 15 illustrate alternate configurations for airfoil shaped tubes. FIG. 14 illustrates a tube 212 of a relatively constant thickness with flow paths 176 disposed along mean camber line B. FIG. 15 illustrates a tube 214 with smaller flow paths 204 disposed near the edges 160 and 162 and larger flow paths 208 disposed near the thicker center section of tube 214. FIG. 16 illustrates a tube 216 employing somewhat larger flow paths 218 in the center section of tube 216 while smaller flow paths 204 are located near the edges 160 and 162. FIG. 17 illustrates a tube 220 with flow paths 204 disposed in a stacked configuration. FIG. 18 illustrates a tube 222 with flow paths 204, 208, and 218 of three different sizes. The smaller size flow paths 204 are located near edges 160 and 162, the larger size flow paths 218 are located within the center section, and the medium size flow paths 208 are located towards trailing edge 162. As will be appreciated, any number of flow path sizes may be included in the airfoil shaped tubes illustrated in FIGS. 10 through 18.

FIG. 19 is a detailed perspective view of a tube and fin configuration employing multichannel tubes 224 with corrugated fins 226. Fins 226 include a series of bends 228 and 230 that provide attachment surfaces for joining fins 226 to multichannel tubes. For example, bends 228 may be brazed or otherwise joined to tube 224, and bends 230 may be joined to another multichannel tube (not shown). Fins 226 include notches, or openings 232 that are aligned to form a path through fins 226. As shown, openings 232 are of a generally circular shape disposed within the bends 228 and 230 to form a semicircular path. However, in other embodiments, the openings may be of any suitable shape such as a square, triangle, or oval. Further, the size of the openings may be varied to adjust the heat transfer rate that occurs between the fins and the external fluid flowing through the fins. According to exemplary embodiments, the openings may be stamped or punched into the fins prior to forming the bends.

Openings 232 are intended to provide a path for condensate to exit the heat exchanger. For example, condensate may collect on the surface of tube 224 and flow down tube 224 through openings 232. Condensate also may collect on fins 226 and flow across the fin surface to openings 232 where it may pass through openings 232 to exit the heat exchanger. According to exemplary embodiments, the multichannel tubes maybe oriented vertically allowing gravity to enhance condensate drainage.

FIG. 20 illustrates an alternate tube and fin configuration employing notched fins 236. Fins 236 include tighter bends 236 and 238 that form relatively parallel fins. Openings 232 provide a path for condensate to exit the heat exchanger. In certain exemplary embodiments, the fins may include a curvature between the bends to direct condensate towards the openings. For example, the fins 240 shown in FIG. 21 include a curvature D disposed between bends 242 and 244. The curvature may be used in conjunction with openings 232 shown in FIG. 20 to direct condensate to openings 232.

In other exemplary embodiments, curved fins 240 may be used in conjunction with a fin manufacturing method that provides trimmed fins as illustrated in FIGS. 22 and 23. FIG. 22 illustrates fins 240 attached to multichannel tubes 224. Bends 242 and 244 of fins 240 extend beyond the plane of tubes 224 by a distance E. The distance E may vary depending on, among other things, manufacturing capabilities. The edges 246 of fins 240 may be brazed or otherwise joined to tubes 224. Bends 242 and 244 may then be trimmed, or removed, to produce independent fins 248, as shown in FIG. 23. According to exemplary embodiments, the bends may be sheared or removed by other suitable means to produce the independent fins. As shown in FIG. 23, independent fins 248 may receive airflow 174 through the openings created by removing the bends. Edges 246 of independent fins 248 extend generally perpendicularly from tubes 224. The generally perpendicular orientation of fins 248 is intended to provide less surface area near tubes 224 for condensate collection. Further, the curved structure of fins 248 may promote condensate drainage.

FIG. 24 illustrates another tube and fin configuration employing fins 252 that may be trimmed. Fins 252 include a series of straight surfaces extending between bends 254. Bends 254 extend outside of the plane of tubes 224 by a distance F. According to exemplary embodiments, the fins may be brazed or otherwise joined to the tubes. Bends 254 may then be trimmed, or removed, to produce independent fins 256, as shown in FIG. 25. Independent fins 256 may receive airflow 174 through the openings created by removing the bends. Although louvers are not shown on the independent fins, louvers may be included in other exemplary embodiments.

FIG. 26 illustrates another tube and fin configuration that may be formed by trimming fins as described above with respect to FIGS. 22 through 25. Independent fins 258 may be brazed or otherwise joined to multichannel tubes 224. Independent fins 258 extend perpendicularly between tubes 224 and include an angled portion 260 intended to promote condensate drainage. Airflow 174 may flow across the fins and direct condensate across the fin surface to angled portion 260. Condensate may then flow down angled portion 260 and be released from the fins. The fins 260 also may include openings 262 to facilitate condensate drainage. In certain exemplary embodiments, the openings may be omitted.

FIG. 27 illustrates a heat exchanger 264 that includes a double header 266. A baffle 272 divides header 266 into two sections 268 and 270. The baffle may be constructed of aluminum or other suitable material. A first set of tubes 274 is fluidly connected to section 270, and a second set of tubes 276 is fluidly connected to section 268. As shown, the first set of tubes 274 and the second set of tubes 276 may constructed from tubes having the same shape that are oriented in different positions. For example, the tubes of the second set 276 may be rotated approximately 180 degrees lengthwise and crosswise prior to insertion into header 266 to direct airflow 174 through heat exchanger 264 in a downward direction. In other exemplary embodiments, the tube configuration shown in FIG. 9 may be used. Further, the shape of the tubes, as well as the flow path configuration, may vary within and between tube sets. Although the multichannel tubes are depicted as having a curved, oblong shape, the tubes may be any shape, such as tubes with a cross-section in the form of a rectangle, square, circle, oval, ellipse, triangle, trapezoid, or parallelogram. In certain exemplary embodiments, the tubes may include the one or more of the configurations illustrated in FIGS. 10 through 18.

FIG. 28 is a top sectional view of the double header shown in FIG. 27. In certain exemplary embodiments, the double header 266 may receive two different phases or refrigerant, one phase within section 268 and another phase within section 270. For example, section 270 may receive refrigerant in a vapor phase while section 268 receives refrigerant in a liquid phase. The separation of refrigerant phases may reduce maldistribution of refrigerant within the header. From section 270, the vapor phase refrigerant 280 may enter flow paths 176 and flow through the first set of tubes 274. From section 268, the liquid phase refrigerant 278 may enter flow paths 176 and flow through the second set of tubes 276. In certain exemplary embodiments, airflow may enter heat exchanger 264 by first passing through the first set of tubes 274 that contain vapor phase refrigerant 278. When a heat exchanger is functioning as an evaporator, a vapor phase refrigerant (which may have a higher temperature) may absorb less heat from an external airflow than a liquid phase refrigerant (which may have a lower temperature) would absorb. The lower amount of heat transfer from the external airflow to the refrigerant, may allow the external airflow to maintain a higher temperature as it flows through the first set of tubes containing vapor phase refrigerant. In certain exemplary embodiment, the higher temperature may result in reduced frost growth on the leading edge of the first set of tubes.

It should be noted that the present discussion makes use of the term “multichannel” tubes or “multichannel heat exchanger” to refer to arrangements in which heat transfer tubes include a plurality of flow paths between manifolds that distribute flow to and collect flow from the tubes. A number of other terms may be used in the art for similar arrangements. Such alternative terms might include “microchannel” and “microport.” The term “microchannel” sometimes carries the connotation of tubes having fluid passages on the order of a micrometer and less. However, in the present context such terms are not intended to have any particular higher or lower dimensional threshold. Rather, the term “multichannel” used to describe and claim embodiments herein is intended to cover all such sizes. Other terms sometimes used in the art include “parallel flow” and “brazed aluminum”. However, all such arrangements and structures are intended to be included within the scope of the term “multichannel.” In general, such “multichannel” tubes will include flow paths disposed along the width or in a plane of a generally flat, planar tube, although, again, the invention is not intended to be limited to any particular geometry unless otherwise specified in the appended claims.

While only certain features and embodiments of the invention have been illustrated and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the invention, or those unrelated to enabling the claimed invention). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation. 

1. A heat exchanger comprising: a first manifold; a second manifold; a plurality of multichannel tubes in fluid communication with the first and second manifolds, being configured to receive an external fluid flowing across a width dimension from a leading edge to a trailing edge, and the multichannel tubes each having an airfoil shape configured to direct condensate of the external fluid from the leading edge to the trailing edge; and a plurality of generally parallel flow paths disposed within each multichannel tube and extending lengthwise through each multichannel tube.
 2. The heat exchanger of claim 1, wherein the airfoil shape is symmetrical, positively cambered, or negatively cambered.
 3. The heat exchanger of claim 1, wherein the generally parallel flow paths comprise different size flow paths.
 4. The heat exchanger of claim 1, wherein the generally parallel flow paths comprise relatively small flow paths disposed near the leading and trailing edges and relatively large flow paths disposed near a center section of each multichannel tube.
 5. The heat exchanger of claim 1, wherein the generally parallel flow paths are disposed along a mean camber line of the airfoil shape.
 6. The heat exchanger of claim 1, wherein at least some of the generally parallel flow paths are disposed above and/or below a mean camber line of the airfoil shape.
 7. The heat exchanger of claim 1, wherein each of the multichannel tubes comprises a cross section that generally tapers outwardly from a maximum thickness towards the leading edge and towards the trailing edge.
 8. The heat exchanger of claim 1, wherein a mean camber line of the airfoil shape slopes more steeply towards the leading edge and less steeply towards the trailing edge.
 9. A heat exchanger comprising: a first manifold; a second manifold; a plurality of multichannel tubes in fluid communication with the first and second manifolds, the multichannel tubes each having a transversely curved cross sectional profile extending from a leading edge to a trailing edge and being configured to receive an external fluid flowing across the transversely cross sectional profile from the leading edge to the trailing edge; and a plurality of generally parallel flow paths disposed within each multichannel tube and extending lengthwise through each multichannel tube.
 10. The heat exchanger of claim 9, wherein the transversely curved cross sectional profile is configured to promote drainage of condensate of the external fluid from the multichannel tubes.
 11. The heat exchanger of claim 9, wherein the transversely curved cross sectional profile comprises an asymmetrical curvature.
 12. The heat exchanger of claim 9, comprising fins for transferring heat to or from the internal fluid flowing through the flow paths during operation, wherein the fins comprise openings encircling the transversely curved cross sectional profiles.
 13. The heat exchanger of claim 9, wherein the multichannel tubes are aligned in two columns within the heat exchanger and wherein the multichannel tubes of each column are staggered with respect to the multichannel tubes of the other column.
 14. The heat exchanger of claim 9, wherein each of the multichannel tubes has a generally convex upper surface and a generally concave lower surface.
 15. A heat exchanger comprising: a first manifold; a second manifold; a plurality of multichannel tubes configured to direct a fluid from the first manifold to the second manifold; and a plurality of fins disposed between the multichannel tubes, each of the fins having wall segments separated by alternating bends attached to the multichannel tubes and having openings disposed through the alternating bends to form a path through the fins.
 16. The heat exchanger of claim 15, wherein the wall segments are generally parallel to one another.
 17. The heat exchanger of claim 15, wherein the wall segments are angled with respect to one another.
 18. The heat exchanger of claim 15, wherein the wall segments are curved toward the openings.
 19. The heat exchanger of claim 15, wherein each of the openings extends through one of the bends and through a portion of the wall segments adjoining the bend.
 20. The heat exchanger of claim 15, wherein the path extends through the fins generally parallel to a length of the multichannel tubes.
 21. A method for making heat exchanger fins, the method comprising: disposing corrugated fins having wall segments separated by alternating bends between multichannel tubes such that the bends extend beyond the multichannel tubes and the edges of the wall segments are disposed against the multichannel tubes; securing the edges of the wall segments to the multichannel tubes to permanently join the wall segments to the multichannel tubes; and trimming the corrugated fins to remove the alternating bends from the corrugated fins and to create openings between the wall segments.
 22. The method of claim 21, wherein trimming the corrugated fins comprises shearing the bends from the corrugated fins to produce individual wall segments.
 23. The method of claim 21, comprising creating openings through the edges of the wall segments.
 24. The method of claim 21, wherein the wall segments are curved.
 25. The method of claim 21, wherein the wall segments are angled.
 26. A heat exchanger comprising: a first manifold having a baffle disposed lengthwise through the first manifold to divide the first manifold into a first section configured to receive a first phase of a refrigerant and a second section configured to receive a second phase of the refrigerant; a second manifold; a first set of multichannel tubes in fluid communication with the first section and the second manifold and configured to direct an external fluid entering the heat exchanger across the first set of multichannel tubes; a second set of multichannel tubes in fluid communication with the second section and the second manifold and configured to direct the external fluid exiting the first set of multichannel tubes across the second set of multichannel tubes; and a plurality of generally parallel flow paths disposed within each multichannel tube of the first and second sets and extending lengthwise through each multichannel tube to direct the refrigerant from the first manifold to the second manifold.
 27. The heat exchanger of claim 26, wherein the heat exchanger comprises an evaporator, the first phase comprises a vapor phase, and the second phase comprises a liquid phase.
 28. The heat exchanger of claim 26, wherein tubes of the first set of multichannel tubes comprise generally straight ends extending into the first section and wherein tubes of the second set of multichannel tubes comprise generally angular ends extending into the second section.
 29. The heat exchanger of claim 26, wherein tubes of the first set of multichannel tubes and the second set of multichannel tubes each comprise a transversely curved cross sectional profile.
 30. The heat exchanger of claim 29, wherein the tubes of the first and second sets of multichannel tubes curve in alternate directions.
 31. The heat exchanger of claim 26, wherein tubes of the first and second sets of multichannel tubes are staggered with respect to one another.
 32. The heat exchanger of claim 26, wherein tubes of the first and second sets of multichannel tubes comprise airfoil shapes. 